1. Field of the Invention
The present invention relates to a color ink-jet recording apparatus that can clearly and densely record color images, and more specifically, to a color ink-jet recording apparatus and method using color ink such as yellow (Y), magenta (M), cyan (C) ink or green (G), red (R), and blue (B) ink as well as black (Bk) ink. The present invention further relates to a method of processing image data used in a color ink-jet recording apparatus.
2. Description of the Related Art
The present invention is applicable to every equipment using recording media such as paper, cloths, and OHP sheets. Specific applied equipment includes, for example, printers, copiers, and facsimile terminal equipment.
Ink-jet recording apparatuses are widely used for printers, copiers, and facsimile terminal equipment because they can be driven with low noise and low running costs and because they allow their sizes to be easily reduced and also allow color ink to be easily introduced.
In general, these color ink-jet recording apparatuses executes color recording using three types of color ink including cyan, magenta, and yellow ink. Alternatively, four types of color ink, that is, the above three types of ink plus black ink may used for color recording.
A conventional ink-jet recording method requires the use of exclusive paper having an ink absorbing layer in order to obtain color images with good coloring and no ink bleeding. However, ink has recently been improved to provide methods adapted for ordinary paper that is used for printers, copiers, and the like in large quantity. However, the grade of recording on ordinary paper still remains at an insufficient level. The greatest factor concerning this situation is the compatibility between the prevention of bleeding between a plurality of ink colors and the grade of black recording (particularly recording of black characters and thin lines).
Typically, if color images are recorded on ordinary paper using an ink-jet recording method, quickly drying ink is used which permeates through ordinary paper at high speed. The use of such ink provides a high-grade image without any ink color bleeding, but in this case, the density of the image is generally low, and what is called feathering is prone to occur in which ink bleeds slightly around each color image along fibers of the paper.
Feathering is relatively unnoticeable in color image areas, whereas it is noticeable in black image areas, thereby reducing the recording grade. In particular, if the black image is a character or a thin line, it will be dull and unclear and thus has a significantly reduced grade.
Thus, to record a black image with reduced feathering and increased density and high quality, black ink must be used which permeates through ordinary paper at a relatively low speed. However, in this case, when the black ink contacts with color ink other than the black ink on a recording medium, bleeding occurs at the boundary between the two types of ink to significantly reduce the recording grade. Thus, the prevention of bleeding between the black ink and the color ink is inconsistent with the improvement of the color image grade achieved by reducing the feathering of the black image. It is now very difficult to make these two requirements compatible. Japanese Patent Application Laid-open No. 4-158049 (1992) proposes a method comprising a plurality of heads for ink that permeates through paper at a relatively high speed for color recording and a head for ink that permeates through paper at a relatively low speed for character recording, wherein the color recording heads and the character recording head are switched depending on a recorded image. However, with this method, the character recording head must be provided separately from the conventional color recording heads, thereby increasing costs and the size of the apparatus.
What is called a divided recording method is known in which an image is formed by causing recording heads to scan the same recording area a plurality of times and in which during a recording process, the number of adjacent dots is reduced to lessen differences between nozzles in the accuracy with which ink from each nozzle impacts a recording media. This divided recording method has been known to be effective in reducing the bleeding. However, even with this divided recording method, bleeding may occur between adjacent images if the images require a relatively large mount of ink to be ejected to a recording medium.